1. Field of the Invention
The present invention relates to a flat panel display and, more particularly, to a high-speed flat panel display having a long lifetime in which thin film transistors of a pixel portion and driving circuit portions have different body contact structures.
2. Description of the Related Art
Generally, an active matrix organic light emitting diode (AMOLED) display includes a pixel portion in which an array of thin film transistors is arranged, and a data driving circuit portion and a gate driving circuit portion for driving the array of thin film transistors in the pixel portion.
In a conventional AMOLED display, the thin film transistors in the pixel portion and thin film transistors in the data or gate driving circuit portion are all composed of polysilicon thin film transistors. Therefore, in a 180 ppi or higher resolution AMOLED display, if the pixel portion and the driving circuit portions are composed of the polysilicon thin film transistors, a high-speed operating characteristic of the driving circuit portions could be obtained because of high mobility of the thin film transistors. However, because an on-current is very high, the amount of a current flowing through EL elements in the pixel portion exceeds a limit value, and thus luminance per unit area increases, which shortens the lifetime of the EL elements.
Meanwhile, when the pixel portion and the driving portions are composed of thin film transistors with low mobility to maintain a suitable on-current characteristic, it results in a relatively low on-current and thus causes appropriate luminance, which overcomes the shortened lifetime problem of the EL element, but it cannot support a high-speed operating characteristic of the driving circuit portions.